To achieve true silver halide photo quality in inkjet printing, multiple levels of black inks need to be used. Within the black inks, light pigment load (gray ink) is necessary for reducing grain and dot visibility, and high pigment load is necessary for high optical density and high color gamut volume.
In photo printing, carbon black is usually the primary ingredient of black pigmented ink. One fundamental limitation with carbon black is “browning” which is the brownish undertone when it is used at low concentration as in a gray ink. This is especially true with the photo grade carbon black.
One way to treat the problems arising from the use of carbon black in black or gray inkjet ink has been to heavily use composite black throughout the color map. Composite black is conventionally the usage of mixtures of cyan, magenta and yellow inks to create neutral gray colors. Composite black has a known set of issues. Color cast/variations are often seen in shadows and fine lines due to drop weight variation, pen alignment and dot placement errors. Metamerism often occurs. Manufacturing variations in drop weight and ink lead to non-neutral black and white tones and color balance problems. This has in turn required closed loop color correction and/or extremely tight manufacturing tolerances.
Another way to deal with the problems of black and gray ink in inkjet has been to use four tones of gray inks. This provides the customer with different shades of black (e.g., warm neutral, cool neutral, selenium, and carbon sepia). However, these inks have not been suitable for glossy photo printing, because they do not stick to glossy paper and they do not provide gloss. A similar system has been produced with dye-based inks, which has had problems with non-permanence and color issues when printed on a range of media.